Atomically thin amorphous materials break free from the constraints of crystalline lattice symmetry, combining two-dimensional geometric features with structural disorder, and exhibit high defect tolerance and continuously tunable physicochemical properties. Unlike two-dimensional crystals stacked via van der Waals forces, amorphous thin films lack grain boundaries and van der Waals gaps, enabling the formation of monolithic films with atomic-level flatness and structural uniformity, which show great application prospects in next-generation integrated circuits, electron transmission, and metal diffusion barrier layers. Currently, the academic community has laid a preliminary foundation in the synthesis and performance exploration of systems such as monolayer amorphous carbon and ultrathin oxides.

However, this field still faces severe challenges when moving toward practical industrial applications. In terms of material synthesis, how to break through the monolayer limitation, precisely control the thickness within the sub-nanometer to several nanometer range, and achieve large-area continuous, pinhole-free uniform growth remains an underexplored challenge. In terms of device integration, semiconductor back-end-of-line processes require a fabrication temperature strictly below 400 °C, while traditional barrier materials tend to fail when thickness is reduced, and two-dimensional crystals are difficult to meet the extremely fine linewidth requirements due to grain boundary and interstitial diffusion. It is necessary to directly grow ultra-thin and highly dense amorphous barrier layers at low process temperatures.

To address the above issues, a team composed of Peking University, the Institute of Physics of the Chinese Academy of Sciences, and others conducted systematic research using ZEPTOOLS' liquid nitrogen cryogenic probe station. The team achieved the controllable preparation of nitrogen-doped amorphous carbon monolithic films with continuously tunable thickness from sub-nanometer to several nanometers, pinhole-free, and with atomic-level flatness through remote plasma-assisted technology, revealing the hydrogen radical bombardment-driven downhill mass transport smoothing growth mechanism, and demonstrating its application potential as a high-performance ultrathin copper diffusion barrier layer compatible with chip back-end-of-line integration processes.

Title: Nitrogen-doped amorphous carbon as atomically thin monolithic membrane
Journal: Matter
URL:http://dx.doi.org/10.1016/j.matt.2026.102911

To address the growth control challenges of two-dimensional amorphous materials, the research team developed a remote plasma-assisted chemical vapor deposition technology, successfully preparing nitrogen-doped amorphous carbon monolithic films with continuously tunable thickness from sub-nanometer to several nanometers. Using pyrazine as the precursor molecule, at substrate temperatures as low as 300 °C to 500 °C, the team achieved a smooth transition from island growth mode to continuous flat film mode by regulating precursor supply and plasma density. The resulting nitrogen-doped amorphous carbon films exhibited pinhole-free, crack-free, and uniform atomic-level flatness at the wafer scale, with root-mean-square roughness as low as 0.36 nm. As a non-layered structural material, it completely overcomes the van der Waals gaps and grain boundary limitations of conventional two-dimensional crystals, forming an atomically thin monolithic membrane with both isotropic structure and high mechanical strength.

In terms of growth mechanism exploration, the research team revealed the hydrogen radical bombardment-driven downhill mass transport smoothing growth mechanism, explaining the physical origin of the difficulty in forming sub-nanometer ultrathin flat films in amorphous materials. Experiments and molecular dynamics simulations showed that hydrogen radicals generated from precursor pyrolysis play a critical role in dynamic etching and surface reconfiguration during deposition. Hydrogen radicals frequently induce the breaking and recombination of near-surface carbon-carbon bonds, endowing atoms with dynamic lateral mobility, effectively counteracting the local protrusions and surface roughening tendencies caused by pure deposition processes. This sustained downhill mass transport mechanism enables the film surface to maintain extreme flatness during continuous growth, providing a new theoretical foundation for the large-area high-quality fabrication of atomically thin amorphous films.

To verify the application feasibility of this material in semiconductor back-end-of-line integration processes, the research team systematically evaluated its electrical performance as a copper diffusion barrier layer. Since the direct deposition temperature of this amorphous carbon film is only 350 °C, it fully meets the temperature limitations of chip back-end processes. The research team constructed capacitor arrays and conducted critical time-dependent dielectric breakdown tests in vacuum and controlled temperature environments using ZEPTOOLS' liquid nitrogen cryogenic probe station. The test data precisely recorded the leakage current evolution and breakdown time of the devices under high electric fields and thermal stress, confirming that even when the thickness of the highly nitrogen-doped amorphous carbon film is reduced to the sub-nanometer level, its mean time to failure is improved by more than tens of times compared to conventional barrier materials, demonstrating excellent barrier performance and long-term reliability.

Combining first-principles density functional theory calculations with multi-scenario functional validation, the research team further elucidated the microscopic mechanism underlying the exceptional performance of nitrogen-doped amorphous carbon films and their broad application prospects. Computational results indicate that nitrogen doping effectively shortens local bond lengths and increases local atomic packing density, producing a significant steric hindrance effect on copper atom diffusion and substantially raising the migration energy barrier for copper atoms. In addition, the film exhibits excellent electron transmission characteristics; after successful transfer onto microchannel plate surfaces, it achieves efficient electron penetration and signal multiplication without dead-zone voltage effects. These results demonstrate that atomically thin nitrogen-doped amorphous carbon films, as high-performance monolithic components, possess tremendous industrial application value in next-generation ultra-large-scale integrated circuit copper interconnect barrier layers, electron detection devices, and molecular barrier applications.

ZEPTOOLS' liquid nitrogen cryogenic probe station is an advanced research instrument specifically designed for high-precision electrical performance testing of semiconductor devices, micro/nano materials, and electronic components under low-temperature environments. It provides ultra-low temperature conditions for samples through a liquid nitrogen refrigeration system, ensuring accurate measurement of electrical characteristics at extremely low temperatures. The equipment is equipped with high-resolution microscope modules that enable clear observation of sample microstructures, facilitating precise alignment and contact between probes and samples. It has been widely applied in various fields including semiconductor R&D, micro/nanoelectronics, materials science, and physical chemistry, serving as an ideal tool for studying temperature-dependent transport properties, thermoelectric performance, photoelectric response, and other key characteristics of devices.